The present invention relates to a reference element to be used for adjusting, calibrating and initializing ultrasonic test equipment for inspecting structural materials.
Extensive equipment for the non-destructive testing of structural material includes, for example, a test stand having at least one, often many, ultrasonic test heads which are to be coupled to the test object for purposes of inspecting the object as to the texture of its interior for purposes of detecting any flaws, inclusions, defects, etc. It is, of course, required that the various test heads in this stand be particularly oriented to the test object as it is going to pass through the stand. Moreover, it is required that the test electronics be adjusted to the particular conditions under which the test is conducted. The test electronics involves particularly the electronic circuitry which processes the ultrasonic signals being received, and that circuitry must be adjusted to the particular conditions under which the test is conducted. The geometric dimensions and propagative properties of the object to be tested and the specific zone therein to be inspected require or make it advisable to launch test pulses along a particular path and into the object for interaction therewith; the interaction may produce a return pulse to be picked up by the same or companion transducer. Depending on the particular conditions, a return pulse may, for example, be an echo from a boundary or an echo from a flaw. The amplitude and time of occurrence of such a return pulse is determined by the propagative properties of the material and by the geometry of the propagative properties. The amplitude is in addition determined by the conditions of its specific production such as the size and orientation of a flaw. On the other hand, the transducer listening to such a response will inevitably pick up noise. It follows therefore that for a specific test task a response to be recognized as a response to an ultrasonic test signal, must have a minimum amplitude to distinguish it from noise, and it must occur wihtin a prescribed period. Thus, the electronics processing the received transducer signal must be adjusted to be responsive to signals of a particular period only (looking window). These are parameters which have to be adjusted before the test can begin.
In application Ser. No. 782,451, filed March 29, 1977, now U.S. Pat. No. 4,106,326, a procedure of initialization, adjusting and calibration is described in detail. This initialization procedure involves in the essence a test body having many similar features as the object to be tested, including in particular the geometry for a test beam path and including further simulated errors so that timing and amplitude of return response signals can be ascertained. For this, a special electronics is used in conjunction with the heads which are positioned and oriented in relation to the test object in exactly the same manner they are expected to be adjusted and oriented later in the test stand. This particular electronics is not the same as the electronics to be used in the test stand but is provided just for ascertaining the necessary parameters under which any electronics is to operate. This initialization electronics will in the following be called preparatory electronics. It will respond to return signals resulting from the interaction of that test pulse with the test body, and the timing and amplitude of that return pulse is ascertained. In conjunction therewith, the period in which such a return signal may occur is ascertained. This alone, however, is not sufficient because as stated, the heads will be installed later in the test stand though under similar orientation and spacing adjustment, but for cooperation with the same type of, but actually a different test stand electronics. Therefore, the initialization procedure requires a standard and reference element to be coupled to the various heads and to be used to invoke a specific response signal to a test pulse. That test pulse launched into the reference body produces a response occurring following a specific transit time and at a particular amplitude, on the basis of the adjusted preparatory electronics. Thereafter, the reference element is used again on the test heads as they are being installed in the final test stand but now in conjunction with the test stand or operational electronics proper; a test signal is launched into this reference body, and its response is being ascertained by and in the test electronics. That response in conjunction with the response previously ascertained when that reference element was used in conjunction with the preparatory electronics, is now used to finally determine the specific parameters of the test electronics in the test stand.